If the fish you have now are young, they alone will max out the capacity of that tank soon enough, without adding more fish.
If they are adults, I would imagine its already maxed, and certain territorial boundaries set.
The braziliensus (if a male) reaches 12"-14".
If the fish are young, and you are going to add more cichlids, you should expect territorial issues from the Geo with any other cichlid later on.
The Geo's can become very aggressive as adults and are not afraid to take on any other cichlid, even if its twice their size.